1. The Field Of The Invention
The present invention relates to heaters useful for the combustion of solid, liquid and gaseous carbonaceous fuels. In one of its more specific embodiments, the invention is concerned with improvements in heat exchangers for use in heaters of this type. The invention is further concerned with an improved system for supplying a heated secondary air source to heaters of the aforesaid type to thereby aid in increasing their efficiency.
2. The Prior Art
In the interest of simplifying the disclosure, the heaters discussed hereinafter will be of the type commonly used for burning solid fuels such as wood. However, it is understood that solid, liquid, liquefiable and gaseous carbonaceous fuels of other types may be used, including, for example, anthracite, bituminous and lignite coals, peat, fuel oils of all types derived from petroleum and renewable sources such as vegetable and animal oils, liquefied normally gaseous fuels such as propane, butane and the like, and natural and artificial gas.
Wood heaters have been in existence for many years and numerous innovations and adaptations have been proposed in an attempt to improve their characteristics. For instance, it has long been known that wood heaters are not as efficient as is desirable. When wood burns in a heater, it releases volatile matter during a first stage of the burning process and then the volatiles burn during the second stage while the solid charcoal remaining from the first stage continues to burn. Once the fire is established, the burning charcoal and gases liberate more combustible gases and volatiles from the wood. In many prior art heater designs, only a relatively small amount of the volatile matter is completely burned and a substantial amount of the combustion products exit the heater unburned or incompletely combusted and enter the atmosphere. The efficiency of wood and other solid fuel heaters depends largely upon the degree of combustion of the volatile products and prior art heaters have been provided with a means for introducing a secondary air supply which causes a more complete combustion process to occur. Examples of such heaters are disclosed in U.S. Pat. Nos. 742,108, 4,047,515, 4,078,541, 4,194,487, 4,201,186 and 4,206,743.
The efficiency of wood and other solid fuel heaters also depends upon the degree to which heat from the combustion of the fuel is transferred to the air or other fluid to be heated. Prior art heat exchange units for heaters are known which comprise a plurality of generally cylindrical tubes through which air is passed and heated. Examples are disclosed in U.S. Pat. Nos. 406,955 and 1,400,299. However, the prior art heat exchange systems for heaters are inefficient and a large percentage of the heat is lost. In heaters with a secondary air supply system, the secondary air supply has been introduced at some point or points remote from the heat exchange unit. In doing so, there is a large efficiency loss.
It is also known in the art to provide a heater with a magazine-type feeding arrangement for the wood or other solid fuel. In such heaters, large supplies of solid fuel such as wood may be supplied above the combustion area and fed toward the combustion area by means of gravity. U.S. Pat. Nos. 2,469,639, 4,194,487 and 4,201,186 disclose examples of such heaters.
The aforementioned and other deficiencies and disadvantages of the prior art heaters have long been recognized by those skilled in this art. However, an entirely satisfactory alternative thereto was not available prior to the present invention in spite of the long existing and great need therefor.